This study investigated potential age and gender differences in the training-related adaptations in muscular force and maximum motor unit firing rates. Young (M = 15; F = 15) and older (M = 15; F = 15) Ss completed two testing sessions, separated by two weeks. During each testing session measures of maximum voluntary contraction force of the dorsiflexors and maximum motor unit firing rates in the tibialis anterior were obtained. During the two-week interval between testing sessions, individuals in the control group were asked to carry out their normal daily activities, while individuals in the training group were asked to participate in a total of six isometric strength training sessions (three per week).

At baseline there were no differences in maximum voluntary contraction force or maximum firing rate between the training and control groups. However, also at baseline, maximum voluntary contraction force was lower in the older Ss when compared to the young and lower in females than in males. The trained group showed a significant 17.8% increase in maximum voluntary contraction force following training, while the control group showed little change (+2.2%). There was no significant Day x Gender or Day x Age interaction, suggesting that young and older males and females showed similar changes in maximum voluntary contraction force in response to training. At baseline, the maximum motor unit firing rate was lower in the older than in the young Ss, and lower in females than in males. The maximum motor unit firing rate increased 14.2 % in the trained group across the two days, while the firing rates in the control group showed a slight 4.3% increase. There was no significant Day x Gender or Day x Age interaction, suggesting that young and older males and females showed similar changes in maximum motor unit firing rate in response to training.

Implication. Although older individuals and females had lower maximum voluntary contraction forces and lower maximum motor unit firing rates than young and male Ss, respectively, they showed similar adaptations in maximum voluntary contraction force and maximum motor unit firing rate in their response to training.